Japanese Laid-Open Patent Publication No. 2010-76022 describes an impact rotation tool that uses an electric motor to tighten and loosen a fastening member such as a bolt. The impact rotation tool includes an impact mechanism that applies a striking impact to an anvil. The anvil is rotated integrally with an output shaft when the motor, which serves as a rotation drive source, rotates. In this type of impact rotation tool, the motor is fixed to a motor seat. The motor seat is held by a housing. The motor is radially and axially positioned by the motor seat and ribs of the housing. The impact mechanism converts the rotation from the motor into a rotation striking impact and transmits the rotation striking impact to the output shaft through the anvil. This transmits impact force to the output shaft, which rotates a bit, so that the fastening member is tightened or loosened with a higher torque.
A resin, a metal, or the like is used as the material of a plate forming the motor seat, which holds the motor. A resin, which may be injection-molded, is used as the material of the housing. When the motor seat and the housing are both a rigid body, striking vibration generated by the impact mechanism is transmitted to the motor without being attenuated at a portion of contact between the housing and the motor seat. Such vibration may cause breakage of a motor coil, breakage of a motor lead line, separation of a magnet, or the like.